The present invention relates to a method for providing uniform pressure, especially to a method for providing uniform pressure to interconnection contacts electrically jointing two circuit boards.
As shown in FIGS. 1A to 1C, the interconnection contacts electrically jointing two circuit boards can be formed by pressing. For example, a flexible circuit board such as a membrane 10a is lapped on a rigid circuit board such as a printed circuit board 20a and an elastomer such as a foam 30a is placed atop the membrane 10a. An upper case 40a and a lower case 50a are placed atop and below the resulting structure. Moreover, a plurality of screws 60a are screwed to the upper case 40a and the lower case 50a to fix both ends of the foam 30a. Therefore, the screws 60a are functioned as fixing points in this structure.
However, in above-mentioned contact structure, the upper case 40a and the lower case 50a have deformation problem and the contacts are subjected to nonuniform pressure due to the retaining action of the screws 60a. The problem is worsened when the interconnection contacts in a high temperature environment. In this situation, the deformation of the upper case 40a and the lower case 50a are more serious and the contacts between the membrane 10a and the printed circuit board 20a have open-circuit problem, as shown in FIGS. 3A and 3B.
To overcome above problem, the foam was developed to have different shape to reduce pressure and to reduce nonuniformity. Alternatively, a metal plate is placed on the foam to reduce nonuniformity. Alternatively, a setting screw is locked on a center portion of the foam, wherein the maximal deformation is occurred. However, the above measures have no satisfactory result.
The problem is exploited by the inventor and it is found that the problem of deformation is caused by the counter action force of the foam exerting on the cases after the screws are tightened. Both ends of the foam function as fulcrum of a lever system and the fixing screws function as force-exerting points. The deformation is increased along an axial line of the foam and has maximum at the center of the foam. Therefore, the ends of the foam have fulcrum effect to the contact structure.
FIG. 2C depicts the deformation of the foam (denoted as y1, y2, . . . etc) along the axial line of the foam (denoted as x1, x2, . . . etc). As can be seen from this figure, in an attempt to reduce deformation of the form at center portion thereof, the locking force of the screw is increased. However, the deformation of cases 40a and 50a is worse as the locking force of the screw is increased, as shown in FIG. 2A.
It is the object of the present invention to provide a method for providing uniform pressure to interconnection contacts such that the deformation due to high temperature process is prevented.
To achieve above object, the present invention provides method provides uniform pressure to contacts electrically jointing a first circuit board and a second circuit board, wherein the first circuit board is lapped on the second circuit board and an elastomer (e.g. a foam) is provided and exerts pressure on the contacts. At least one fixing point is provided atop the transverse of the elastomer to uniformly distribute a pressing force of the foam on the contacts.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: